Various fuel systems may be used to deliver a desired amount of fuel to an engine for combustion. One type of fuel system includes a port fuel injector and a direct injector for each engine cylinder. The port injectors may be operated during engine starting to improve fuel vaporization and reduce engine emissions. The direct injectors may be operated during higher load conditions to improve engine performance. In addition, both port injectors and direct injectors may be operated under some conditions to leverage advantages of both types of fuel delivery.
Direct injection fuel systems may include a high pressure fuel pump upstream of a fuel rail to raise a pressure of the fuel delivered to the engine cylinders through the direct injectors. However, when the high pressure fuel pump is turned off, such as when no direct injection of fuel is requested, pump durability may be affected. Specifically, the lubrication and cooling of the pump may be reduced while the high pressure pump is not operated, thereby leading to pump degradation.
Various approaches have been developed to reduce high pressure pump degradation. In one approach, as shown by Faix et al. in U.S. Pat. No. 6,230,688, a constant fuel lubrication flow quantity is branched off from the delivery flow of a low pressure pump coupled to a fuel tank, and delivered to a high pressure pump.
However, the inventors herein have identified a potential issue with such an approach. As one example, when the fuel tank becomes empty or the fuel level in the fuel tank falls below a threshold, the constant lubrication flow may not be available. Consequently, the high pressure pump may degrade. In particular, in dual fuel systems where the fuel tank coupled to the direct injection system is smaller than the fuel tank coupled to the port injection system, the fuel tank may become empty more often, leading to frequent disabling of the high pressure pump. As such, this may reduce the reliability of the high pressure pump.
Thus, in one example, the above issue may be at least partly addressed by a method of operating an engine fuel system. In one embodiment, the method comprises, supplying a first type of fuel solely from a first fuel tank to a second fuel pump and to a group of port fuel injectors via a first fuel pump, an output of the second fuel pump in communication with a group of direct injectors, and supplying the first type of fuel from an outlet of the second fuel pump to the group of port fuel injectors.
In one example, an engine may include a dual fuel system with a first fuel tank storing a first fuel type (such as, gasoline) and a second fuel tank storing a second fuel type (such as an alcohol blend like E85). A first group of port injectors in communication with a group of cylinders of the engine may be configured to port inject fuel into the group of cylinders. A second group of direct injectors also in communication with the group of cylinders may be configured to direct inject fuel into the group of cylinder. A first low pressure pump, in communication with the first fuel tank, may be operated to deliver the first fuel type along a first fuel passage to a first common rail of the first group of port injectors. Similarly, a second low pressure pump, in communication with the second fuel tank, may be operated for delivering the second fuel type along a second fuel passage to a second common rail of the second group of direct injectors. In one example, the low pressure fuel pumps may be electrically-driven.
The fuel system may also include a high pressure fuel pump, the output of the high pressure pump communicating with the first and second group of injectors, may be provided along the second fuel passage. In one example, the high pressure fuel pump may be mechanically driven. The high pressure fuel pump may communicate with the second group of direct injectors via the second common rail, and may further communicate with the first group of port injectors via a solenoid valve and the first common rail. During selected engine operating conditions, such as when direct injection of a fuel (first or second fuel type) is requested, the high pressure pump may be operated in addition to the low pressure pump corresponding to the fuel type so as to raise a pressure of the fuel delivered to the second common rail and through the direct injectors, thereby delivering a high pressure direct injected fuel into the group of cylinders.
The fuel system may further include a first bypass passage coupling the first fuel passage to the second fuel passage upstream of the high pressure pump, and a second bypass passage coupling the first fuel passage to the second fuel passage downstream of the high pressure pump. The second bypass passage may include a solenoid valve, such as an electronically controlled solenoid valve, coupling the first fuel passage to the second fuel passage, downstream of the high pressure pump, when the valve is opened. Thus, when opened, the output of the high pressure pump can communicate with the first group of port injectors via the solenoid valve. In comparison, when closed, the high pressure pump can communicate with the second group of direct injectors.
Based on engine operating conditions, operation of one or more of the low pressure pumps coupled to the first and second fuel tanks, as well as operation of the high pressure pump may be adjusted, while also adjusting the opening of the solenoid valve, to thereby provide fuel to the group of cylinders via the first and/or second group of injectors while enabling sufficient cooling and/or lubrication of the high pressure pump.
For example, based on engine operating conditions, as well as an amount of fuel available in each of the first and second fuel tanks, a first amount of the first fuel type may be port injected into the cylinders. Accordingly, the first low pressure pump may be operated to supply the first fuel to the group of port injectors via the first fuel pump only. In another example, based on operating conditions, a second amount of the second fuel type may be direct injected into the cylinders. Accordingly, the second low pressure pump may be operated to supply the second fuel to the high pressure pump, and the high pressure pump may be operated to raise the pressure of the received second fuel. The higher pressure fuel may then be supplied from an outlet of the high pressure pump to the second group of direct injectors. As such, when direct injection is enabled, the flow of fuel through the high pressure pump enables sufficient cooling and lubrication of the high pressure pump.
During selected engine operating conditions, such as when no direct injection of fuel is requested but cooling and/or lubrication of the high pressure pump is required (such as due to the pump temperature exceeding a threshold temperature and/or a duration of pump operation exceeding a threshold duration), fuel may be port injected into the group of cylinders via the high pressure pump. Specifically, the first low pressure pump may be operated to supply solely the first fuel type from the first fuel tank to the high pressure pump, and the high pressure pump may be operated to supply solely the first fuel type from an outlet of the high pressure pump to a first group of port injectors via the (open) solenoid valve. An output of the high pressure pump may be coordinated with the output of the first low pressure pump to provide a desired fuel rail pressure at the first common rail of the first group of injectors, and to adjust the amount of fluid circulated through the high pressure pump. At the same time, the second low pressure fuel pump and the second group of direct injectors may be deactivated. In this way, by supplying at least some of the first fuel type to the first group of injectors via the high pressure pump, the high pressure pump may be maintained lubricated and cooled even when no direct injection is requested, thereby reducing high pressure pump degradation.
In another example, when direct injection of the second fuel type is requested, but the level of second fuel in the second fuel tank is below a threshold, the first fuel type may be supplied to the group of direct injectors via the high pressure pump to compensate for the second fuel as well to reduce degradation of the high pressure pump due to fuel insufficiency. Specifically, if the fuel level in the second fuel tank is below the threshold, and high pressure pump cooling and/or lubrication is required, then the first low pressure pump may be operated to supply solely the first fuel type from the first fuel tank to the high pressure pump, and the high pressure pump may be operated to supply solely the first fuel type from the high pressure pump to the group of direct injectors. Herein, the solenoid valve may remain closed. The controller may determine an amount of first fuel to be direct injected that compensate for the amount of second fuel that was to be direct injected and further to account for high pressure pump cooling and lubrication. Additionally, in case of a sudden surge in cylinder fuel demand, such as during cylinder enrichment, the solenoid valve may be opened and at least some of the first fuel may also be delivered from the high pressure pump to the first group of port injectors via the solenoid valve so the direct injection of the first fuel is supplemented with the port injection of the first fuel. In this way, by flowing fuel of the first fuel type through the high pressure pump when an insufficient amount of second fuel is available, lubrication and cooling of the high pressure pump is enabled.
In this way, by circulating at least some fuel from a first fuel tank through the high pressure pump when no direct injection is required, and/or when no fuel from the second tank (coupled to the direct injector) is available, a high pressure pump may be maintained lubricated and cooled, thereby reducing high pressure pump degradation. Furthermore, by reducing the need to disable the high pressure pump due to insufficient availability of second fuel and/or no need for direct injection, high pressure pump reliability may be improved.